added Key.h to plist++ header file
diff --git a/include/plist/plist++.h b/include/plist/plist++.h
index d5eb691..0690b26 100644
--- a/include/plist/plist++.h
+++ b/include/plist/plist++.h
@@ -31,6 +31,7 @@
 #include "Integer.h"
 #include "Node.h"
 #include "Real.h"
+#include "Key.h"
 #include "String.h"
 #include "Structure.h"